Focal plane shutter

ABSTRACT

A focal plane shutter includes a reversing lever mounted on a shaft disposed on a driving lever for opening and closing a blade group constituting the focal plane shutter so that a relative rotation range of the reversing lever with respect to the driving lever is restricted. Energizing means for energizing the driving lever toward the end of forward movement is directly engaged with the reversing lever. Further, a cam follower is disposed on the reversing lever between the shaft mounting the reversing lever and the engagement point of the reversing lever with the energizing means. Energizing force acting on the reversing lever is transmitted to the driving lever through the reversing lever to move the driving lever toward the end of forward movement. Motion of the cam follower is restrained by a cam profile while the driving lever is moved toward the end of forward movement, so that the energizing force acting on the reversing lever is reversed at the cam follower serving as a fulcrum and is transmitted to the driving lever as braking force. Accordingly, shock and oscillation at the end of forward movement are reduced.

BACKGROUND OF THE INVENTION

The present invention relates to a driving mechanism for a focal planeshutter, and more particularly to a driving mechanism for a focal planeshutter provided with a shock absorption mechanism capable ofeffectively absorbing shock at the end of forward movement of each bladegroup constituting the focal plane shutter with a simple structure.

A focal plane shutter for a recent single lens reflex camera attainshigh-speed operation of shutter blades in order to stabilize theexposure accuracy in a short exposure time and increase thesynchronization speed of the electronic flash.

For example, a shutter was moved across a vertical distance of 24 mmfrom an upper end to a lower end of an aperture of a frame of a 35 mmtype camera in about 7 ms several years ago, whereas it has been adaptedto be moved in about 3 ms recently.

On the other hand, it is well known that operation sound and oscillationat the end of forward movement of the shutter blades are increased asthe blade speed is increased. A focal plane shutter having a high bladespeed requires an effective shock absorption mechanism.

A conventional shock absorption mechanism which includes a brake leverdisposed in a path through which a blade driving member passes andpressed between a friction plate and a leaf spring so that the brakelever is rotated by striking the blade driving member against the brakelever and the kinetic energy of the blade driving member and the shutterblades is converted into thermal energy by friction of the frictionplate and the brake lever to absorb shock is generally known.

However, the above-mentioned friction type shock absorption mechanismhas many problems as described below.

The coefficient of friction between the members is effected by variationin temperature and aging and accordingly the shock absorptionperformance tends to be varied.

Since the brake lever and the friction plate for the shock absorptionare provided in addition to the shutter driving mechanism, the number ofcomponents are increased and the space factor is reduced.

The shock absorption mechanism must also be set at the time of thesetting operation in addition to the shutter driving mechanism andaccordingly the setting force is increased.

U.S. Pat. No. 4,975,722 discloses a mechanism for utilizing a singlespring as a source of driving force and a source of braking force.However, in accordance with this patent, since a blade driving lever 18and blade brake lever 15, the number of components is increased and thespace factor is reduced.

BRIEF SUMMARY OF THE INVENTION

The present invention has been made in view of the above problem, and itis an object of the present invention to provide a driving mechanism fora focal plane shutter including a shock absorption mechanism havingstable shock absorption performance, reduced space requirements and nonecessity of increasing the setting force.

The driving means of the present invention is used with a focal planeshutter including a blade group for opening and closing the aperturewhich is formed in a shutter base plate.

The blade group includes a plurality of individual blades and is drivenby a driving lever between the unfolded state for closing the apertureand the overlapped state for opening the aperture.

The driving lever is swingably mounted about an axis which is disposedon the base plate.

According to the present invention, a reversing lever is swingablymounted about an axis disposed on the driving lever at a positiondifferent from the axis about which the driving lever itself isswingable and the reversing lever has a restricted relative rotationrange with respect to the driving lever. Furthermore, an operation endof a driving spring is engaged with a free end of the reversing lever tourge the reversing lever toward an end of forward movement of thedriving lever. Accordingly, the force exerted by the driving spring istransmitted to the driving lever through the reversing lever.

More particularly according to the present invention, the force exertedby the driving spring is transmitted to the driving lever through thereversing lever as a driving force in a former region of a movement pathof the driving lever and as a braking force in a latter region of themovement path of the driving lever.

A cam follower is disposed on the reversing lever between the axisaround which the reversing lever swings and the free end of thereversing lever and with which the driving spring is engaged. Themovement of the reversing lever is controlled by the cam profile of acam means.

This cam profile includes a first portion for leading the cam followeralong an arcuate locus about the axis of pivoting of the driving leverin a former region of the movement path of the driving lever from aninitial position of the driving lever to the end of forward movement,and a second portion for restraining the rotation of the cam followerabout the axis of pivoting of the driving lever in a latter region ofthe movement path of the driving lever from the initial position of thedriving lever to the end of forward movement.

Furthermore, the driving lever is attracted to a releasing magnet at itsinitial position.

Accordingly, when the driving lever is released and is moved from theinitial position of the driving lever toward the end of forwardmovement, the reversing lever is moved together with the driving lever,and the cam follower provided on the reversing lever is moved along thearcuate locus about the axis of pivoting of the driving lever in theformer region of movement of the driving lever.

The cam follower provided on the reversing lever comes into contact withthe second cam profile portion before the driving lever reaches the endof forward movement.

The driving lever continues to be moved by the force of inertia evenafter the cam follower has come into contact with the second portion,while, since the cam follower is disposed between the point at which thereversing lever is mounted on the driving lever and the point at whichthe driving spring is engaged therewith, the force of the driving springis reversed with the cam follower serving as a fulcrum and istransmitted to the driving lever after the cam follower has come intocontact with the second cam profile portion. Accordingly, a brakingforce is exerted on the driving lever and shock and oscillation at theend of forward movement are reduced.

Accordingly, in the present invention, since a single driving spring isutilized as a source of driving force for moving the driving lever untilthe middle of movement of the driving lever and is utilized as a sourceof force for braking the driving lever from the middle of the movementof the driving lever, it is not necessary to provide a braking springseparately, and space for locating a braking mechanism is reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a peripheral mechanism of shutter blades of afocal plane shutter according to an embodiment of the present invention;

FIG. 2 is a plan view showing a shutter driving mechanism in a shutterset state according to an embodiment of the present invention;

FIG. 3 is a sectional view of a driving mechanism of a first blade sidein the mechanism shown in FIG. 2;

FIG. 4 is a partial plan view of the mechanism shown in FIG. 2;

FIG. 5 is a partial plan view of the mechanism shown in FIG. 2 in whichthe first blade has not started to move;

FIG. 6 is a partial plan view of the mechanism shown in FIG. 2 in whichthe first and second blades are engaged at the end of forward movement;

FIG. 7 is a partial plan view showing the mechanism in which theengagement of the first blade at the end of forward movement isreleased;

FIG. 8 is a partial plan view showing the mechanism shown in FIG. 2 inwhich the engagement of the second blade at the end of forward movementis released;

FIG. 9 is a plan view of a shutter driving mechanism in a shutter setstate according to another embodiment of the present invention;

FIG. 10 is an enlarged view of a driving mechanism of a first blade sidein the mechanism shown in FIG. 9;

FIG. 11 is an enlarged view of a driving mechanism of a second bladeside in the mechanism shown in FIG. 9; and

FIG. 12 is a sectional view showing a mounting structure of a cam plateof the second blade side in the mechanism shown in FIG. 9.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will now be described in detailwith reference to the drawings.

FIG. 1 is a plan view showing an initial state of blade groups includinga first blade group 1 and a second blade group 2 for a focal planeshutter according to an embodiment of the present invention, couplinglevers 3 and 4 for moving the first blade group 1 and coupling levers 5and 6 for moving the second blade group 2.

In the initial state, the first blade group 1 is in the spread state andthe second blade group 2 is in the overlapped state. Accordingly, in theinitial state, an aperture 7a for exposure formed in the middle of abase plate 7 is closed by the first blade group 1. The base plate 7 isdisposed in front of mechanical members shown in FIG. 1 and thus thebase plate 7 is shown by a one-dot chain line in phantom in FIG. 1.

The coupling levers 3 and 4 are swingably supported on the base plate 7by means of shafts 8 and 9, respectively.

Blades 1a, 1b, 1c and 1d constituting the first blade group 1 arerotatably mounted on the coupling lever 3 by means of machine screws 3a,3b, 3c and 3d, respectively, and also rotatably mounted to the couplinglever 4 by means of machine screws 4a, 4b, 4c and 4d, respectively. Thecoupling levers 3 and 4 together with each of the blades 1a, 1b, 1c and1d form a parallel linkage.

A bend portion 10 (described later) extending into a slot 7b formed inthe base plate 7 is engaged with the coupling lever 3. When the bendportion 10 is moved down along the slot 7b, the coupling lever 3 isrotated clockwise about the axis 8 and the coupling lever 4 is alsorotated clockwise about the axis 9 in interlocked relationship with therotation of the coupling lever 3 so that the blades 1a, 1b, 1c and 1dare moved downward to open the aperture 7a.

Similarly, the coupling levers 5 and 6 are swingably supported on thebase plate 7 by means of the shafts 11 and 12, respectively.

Blades 2a, 2b, 2c and 2d are rotatably mounted on the coupling lever 5by means of machine screws 5a, 5b, 5c and 5d, respectively, and alsorotatably mounted on the coupling lever 6 by means of machine screws 6a,6b, 6c and 6d, respectively. The coupling levers 5 and 6 together witheach of the blades 2a, 2b, 2c and 2d form a parallel linkage.

A bend portion 30 extending into a slot 7c formed in the base plate 7 isengaged with the coupling lever 5. When the bend portion 30 is moveddown along the slot 7c, the coupling lever 5 is rotated clockwise aboutthe shaft 11 and the coupling lever 6 is rotated clockwise about theshaft 12 in interlocked relationship with the rotation of the couplinglever 5 so that the blades 2a, 2b, 2c and 2d are moved down to close theaperture 7a.

In such a focal plane shutter, a time difference between the start ofthe movement of the first blade group 1 and the start of the movement ofthe second blade group 2 corresponds to the exposure time. Thus, inorder to stabilize the exposure accuracy for a short exposure time andincrease the synchronization speed of the electronic flash, it isnecessary to increase the velocity of movement of the first and secondblade groups 1 and 2.

However, when the velocity of movement of the blade groups is increased,strong shock and oscillation are produced at the end of forward movementof the blade groups.

The present invention provides a novel shock absorption mechanism forabsorbing shock at the end of forward movement. Its actual structurewill now be described with reference to the first embodiment shown inFIGS. 2-8 and the second embodiment shown in FIGS. 9-12.

Further, mechanical elements shown in FIGS. 2-8 include many elementsenergized by springs. However, in order to avoid complicating thedrawings, springs other than important springs are illustrated only byarrows indicating the force direction.

First of all, a driving mechanism for the first blade group isdescribed.

A first blade driving lever 15 having a rear surface on which theabove-described bend portion 10 is formed is swingably supported on ashaft 14 disposed on the base plate 7. A reversing lever 16 is swingablymounted on a shaft 15a disposed on the rear surface of the first bladedriving lever 15. The reversing lever 16 serves to transmit drivingforce to the first blade group 1 in the first half region or the formerregion of the movement of the first blade group 1 and to transmitbraking force to the first blade group 1 in the second half region orthe latter region.

A bend portion 18a formed at an end of the reversing lever 16 extendsinto a hole 15b formed in the first blade driving lever 15. Accordingly,the relative range of rotation of the reversing lever 16 with respect tothe first blade driving lever 15 is restricted by the hole 15b.

A free end 17a of a driving torsion spring 17 is engaged with the bendportion 16a and a fixed end of the torsion spring 17 is engaged with apin 18 fixedly mounted to a camera body (not shown).

Accordingly, force exerted on the reversing lever 16 by the torsionspring 17 is transmitted to the first blade driving lever 15 asclockwise rotation force about the shaft 14 through the bend portion 16aand an edge 15c (see FIG. 4 et seq) of the hole 15b.

A cam follower 19 having the function of a set roller is rotatablymounted on the rear surface of the reversing lever between the shaft 15aand the bend portion 16a. A cam means in the form of a groove cam 20that the cam follower 19 follows is formed in the base plate 7.

A first arcuate cam profile portion 20a (see FIG. 4 et seq) for leadingthe cam follower 19 along a circular arc about the shaft 14 is formed inthe first half portion of the groove cam 20 while a second cam profileportion 20b for restraining continuation of rotation of the cam follower19 about the swinging shaft 14 of the first blade driving lever 15 isformed in the second half portion of the groove cam 20.

The embodiment is characterized in that the shape of the groove cam 20is formed so that the cam follower 19 reaches the second cam profileportion 20b from the first portion 20a of the groove cam 20 before thefirst blade driving lever 15 is moved to the end of forward movement inthe clockwise rotation of the first blade driving lever 15 itself.Further, the embodiment is further characterized in that the groove cam20 is formed in the shape of an obtuse angle defined by tangent lines tothe first portion 20a and the second portion 20b at a connection pointthereof.

A driving mechanism for the second blade group will now be described.

In the embodiment, the driving mechanism for the second blade group issubstantially the same as the driving mechanism for the first bladegroup and accordingly elements of the driving mechansim of the secondblade group are designated by reference numerals obtained by adding "20"to the reference numerals given to the corresponding elements of thedriving mechanism of the first blade group to simplify the description.

A second blade driving lever 35 having a rear surface on which theabove-described bend portion 30 is formed is swingably supported on ashaft 34 of the base plate 7 and a rversing lever 36 is swingablymounted on a shaft 35a on the rear surface of the second blade drivinglever 35.

A bend portion 36a formed at an end of the reversing lever 36 extendsinto a hole 35b formed in the second blade driving lever 35 andaccordingly the relative range of rotation of the reversing lever 36with respect to the second blade driving lever is restricted by the hole35b.

A free end 37a of a driving torsion spring 37 is engaged with the bendportion 36a and a fixed end of the torsion spring 37 is engaged with apin 38.

Accordingly, force exerted on the reversing lever 36 by the torsionspring 37 is transmitted to the second blade driving lever 35 throughthe bend portion 36a and edge 35c (see FIG. 4 et seq) of the hole 35b asclockwise rotation about the shaft.

A cam follower is mounted on the rear surface of the reversing lever anda groove cam 40 that the cam follower 39 follows is formed in the baseplate 7.

A first cam profile portion 40a for leading the cam follower 39 along acircular arc about the shaft 34 is formed in the first half portion ofthe groove cam 40 while a second portion 40b for restrictingcontinuation of rotation of the cam follower 39 about the swinging shaft39 is formed in the second half portion of the groove cam 40.

Reference numeral 41 denotes a set lever for initializating theoperation of the shutter mechanism.

The set lever 41 is swingably supported on a shaft 42 and is coupledwith a set cam 44 through a set link 43. Further, counterclockwise forceis exerted on the set lever 41 by a spring S1.

When the set lever 41 is rotated clockwise about the shaft 42 againstthe counterclockwise force of the spring S1, the set cam 44 is rotatedclockwise about a shaft 45.

A cam surface 44a formed on the set cam 44 abuts against theabove-described cam follower 19 in the clockwise rotation of the set cam44 to rotate the first blade driving lever 15 counterclockwise. A camsurface 44b formed on the set cam 44 abuts against the above-describedcam follower 39 in the clockwise rotation of the set cam 44 to rotatethe second blade driving lever 35 counterclockwise.

Numeral 46 designates a first blade stopper for engaging the first bladedriving lever 15 when the first blade group finishes movement, andnumeral 47 designates a second blade stopper for engaging the secondblade driving lever when the second blade group finishes movement. Thefirst and second blade stoppers 46 and 47 are on shafts 48 and 49,respectively. Clockwise rotation force is exerted on the first andsecond blade stoppers 46 and 47 by springs S2 and S3, respectively. Thedetailed operation of the first and second blade stoppers 46 and 47 isdescribed later. Numerals 50 and 51 designate magnets forelectromagnetic release.

Operation of the embodiment will now be described with reference to theforegoing description.

In the initial state, the peripheral mechanism of the shutter blade isin the state shown in FIG. 1 and its driving mechanism is in the stateshown in FIGS. 2 and 4.

In the initial state, the counterclockwise rotation force exerted on theset lever 41 by the spring S1 is transmitted to the set cam 44 throughthe set link 43 as counterclockwise rotation force, while the set cam 44is engaged with a mechanical release lever (not shown) and thecounterclockwise rotation of the set cam 44 is restricted in the stateof the apparatus as shown in FIGS. 2 and 4.

When the set cam 44 is released form the release lever (not shown) inthe state of FIG. 2, the counterclockwise rotation force exerted on theset lever 41 by the spring S1 is transmitted to the set cam 44 throughthe set link 43 to rotate the set cam 44 counterclockwise.

When the set cam 44 is rotated counterclockwise, the cam surface 44a ofthe set cam 44 is separated from the cam follower 19 for the first bladegroup and the cam surface 44b of the set cam 44 is separated from thecam follower 39 for the second blade group.

Accordingly, the reversing lever 16 is rotated counterclockwise aboutthe shaft 15a by the force of the torsion spring 17 so that the bendportion 16a abuts against the edge 15c of the hole 15b formed in thefirst blade driving lever 15 to exert clockwise rotation force on thefirst blade driving lever 15. Similarly, the reversing lever 36 isrotated counterclockwise about the shaft 35a by the force of the torsionspring 37 so that the bend portion 36a abuts against the edge 35c of thehole 35b formed in the second blade driving lever 35 to exert clockwiserotation force on the second blade driving lever 35.

The state at this time is shown in FIG. 5.

However, in the state shown in FIG. 5, since an iron piece 15d providedon the first blade driving lever 15 is attracted to the magnet 50 and aniron piece 35d provided on the second blade driving lever 35 isattracted to the magnet 51, the first and second blade groups 1 and 2are maintained in the initial state.

After the set cam 44 is released, the magnets 50 and 51 are sequentiallydemagnetized with a time difference corresponding to an exposure time.

With the first blade group, the force of the spring 17 is transmitted tothe first blade driving lever 15 through the bend portion 16a of thereversing lever 16 and the edge 15c of the hole and the first bladedriving lever 15 is rotated clockwise about the axis 14.

Accordingly, since the bend portion 10 formed on the rear surface of thefirst blade driving lever 15 is moved down along the slot 7b, thecoupling lever 3 is rotated clockwise about the shaft 8 and the couplinglever 4 is also rotated clockwise about the shaft 9 in interclockedrelationship with the rotation of the coupling lever 3. Accordingly, theblades 1a, 1b, 1c and 1d constituting the first blade group 1 are moveddown to open the aperture 7a.

Since the first cam profile portion 20a having a circular arc about theshaft 14 is formed in the first half portion of the groove cam 20, thereversing lever 16 is rotated about the shaft 14 together with the firstblade driving lever 15 as far as the cam follower 19 passes along thefirst portion 20a.

While the reversing lever 16 is rotated together with the first bladedriving lever 15, the cam follower 19 approaches from the first portion20a to the second portion 20b of the groove cam 20 before the firstblade driving lever 15 reaches the end of forward movement.

After the cam follower 19 reaches the second portion 20b, the firstblade driving lever 15 continues to be rotated to the end of forwardmovement by the force of inertia of the first blade driving lever 15itself and the force of inertia of the mechanism associated with thefirst blade group 1. Thus, the portion of the shaft 15a of the reversinglever 16 continues to be rotated together with the first blade drivinglever 15.

On the other hand, the rotation of the portion of the cam follower 19about the shaft 14 is restrained by the second cam profile portion 20band accordingly the reversing lever 16 is rotated clockwise about theshaft 15a relatively to the first blade driving lever 15. Thus, sincethe bend portion 16a formed on the reversing lever 16 is separated fromthe edge 15c of the hole 15b of the first blade driving lever 15, theclockwise rotation force of the torsion spring 17 is no longertransmitted to the first blade driving lever 15.

Furthermore, even at this time, since the free end of the torsion spring17 is engaged with the bend portion 16a of the reversing lever 16, theforce exerted by the torsion spring 17 on the bend portion 16a of thereversing lever 16 is reversed at the cam follower 19 serving as afulcrum and is transmitted to the shaft 15a of the reversing lever 16.Accordingly, the force is exerted on the first blade driving lever 15 asa counterclockwise rotation force (that is, braking force) about theshaft 14.

In this manner, in the embodiment, the first blade driving lever 15 ismoved to the end of forward movement by the force of inertia of thelever 15 itself and the mechanism associated with the first blade groupeven after the cam follower 19 has approached the second cam profileportion 20b from the first portion 20a of the groove cam 20, althoughthe force from the torsion spring 17 is not exerted and is reversed bythe reversing lever 16 to be transmitted as the braking force after thecam follower has approached the second cam profile portion 20b from thefirst portion 20a of the groove cam 20, shock and oscillation at the endof movement is greatly reduced.

Then, an engagement projection 15e formed on the first blade drivinglever 15 is engaged with the first blade stopper 48 so that the firstblade driving lever 15 is stopped.

The operation of the driving mechanism of the second blade group isquite the same as that of the first blade group, and an engagementprojection 35e formed on the second blade driving lever 35 is engagedwith the second blade stopper 47 so that the second blade driving lever35 is stopped.

The state at this time is shown in FIG. 6.

As described above, after the exposure operation has been finished, theset lever 41 is rotated clockwise about the shaft 42 against the forceof the spring S1 in interlocked relationship with a film windingoperation performed by a motor or manually, so that the set cam 44 isrotated clockwise through the set link 43.

Since the cam surface 44c formed on the set cam 44 rotates the firstblade stopper 46 about the shaft 48 in response to the clockwiserotation of the set cam 44, the engagement between the first bladestopper 46 and the engagement projection 15e of the first blade drivinglever 15 is released.

At this time, since the force of the torsion spring 17 reversed by thereversing lever 16 at the cam follower 19 serving as a fulcrum istransmitted to the first blade driving lever 15, the first blade drivinglever 15 is rotated counterclockwise until the edge 15c of the hole 15bcomes into contact with the bend portion 16a of the reversing lever 16.The state at this time is shown in FIG. 7.

When the set cam 44 is further rotated clockwise, the cam surface 44dformed on the set cam 44 rotates the second blade stopper 47counterclockwise about the shaft 49 and accordingly the engagementbetween the second blade stopper 47 and the engagement projections 35eof the second blade driving lever 35 is released. Thus, the second bladedriving lever is also rotated counterclockwise by the force of thetorsion spring 37 until the edge 35c of the hole 35b comes into contactwith the bend portion 36a of the reversing lever 36. The state at thistime is shown in FIG. 6.

In the embodiment, since there is a slight time difference between therelease of the engagement in the first blade group and the second bladegroup, there is no possibility that the aperture for exposure is openedduring the returning of the blade groups.

Thereafter, when the set cam 44 is further rotated clockwise, the camsurface 44a formed on the set cam 44 abuts against the cam follower 19for the first blade group and the cam surface 44b formed on the set cam44 abuts against the cam follower 39 for the second blade group, so thatthe first blade driving lever 15 and the second blade driving lever 35are rotated counterclockwise to return to the initial state shown inFIGS. 2 and 4.

A second embodiment shown in FIGS. 9-12 will now be described. Portionsof the second embodiment corresponding to those of the first embodimentare designated by the same reference numerals as those in the firstembodiment, and duplicate description is omitted. Elements differentfrom the first embodiment are described.

In the first embodiment, the moving loci of the cam followers 19 and 39are restricted by the groove cams 20 and 40 formed in the base plate 7,while in the second embodiment the moving loci of the cam followers 19and 39 are respectively restricted by cam means in the form of a camplate 60 for the first blade group and a cam plate 80 for the secondblade group fixedly mounted to the base plate 7.

In addition, in the second embodiment shown in FIGS. 9-12, two methodsof mounting the cam plate 60 for the first blade group and the cam plate80 for the second blade group are illustrated.

The cam plate 60 for the first plate blade group is fixedly mounted tothe base plate 7 by means of the shaft 42 of the set lever 41 and theshaft 14 of the first blade driving lever 15.

Formed on the cam plate 60 is a cam profile 60a for restricting the camfollower 19 from continuing the arcuate rotation about the shaft 14 inthe second half part of the clockwise rotation of the first bladedriving lever 15. The cam profile 60a is formed at a position in whichthe cam follower 19 abuts against the cam profile 60a before the firstblade driving lever 15 reaches the end of forward movement, and theshape of the cam profile 60a is set so that a tangent line of the movinglocus formed by the cam follower 19 just before the cam follower 19comes into contact with the cam profile 60a intersects the cam profile60a in an obtuse angle. The cam profile 60a performs the same operationas that of the second profile portion 20b of the groove cam 20 of thefirst embodiment.

The method of mounting the cam plate 80 of the second blade group on thebase plate 7 is different from that of the cam plate 60 of the firstblade group.

More particularly, the cam plate 80 of the second blade group is fixedlymounted on the base plate 7 so that the position of the cam plate 80 canbe adjusted by the shafts 34 and 82 of the second blade driving lever35.

FIG. 12 is a sectional view showing a portion of the shaft 82. A groove82a for adjustment is formed in a head of the shaft 82. The shaft 82extends through an adjustment groove 80b formed in the cam plate 80 andis screwed into the base plate 7. Since the shaft 82 is formed with aneccentric part 82b having a diameter equal to that of an inner diameterof the adjustment groove 80b, the cam plate 80 can be rotated by aslightly small angle about the shaft 34 by properly rotating the shaft82 by means of a tool inserted into the groove 82a.

Formed on the cam plate 80 is a cam profile 80a for restricting the camfollower 39 from continuing the rotation about the shaft in the secondhalf of the clockwise rotation of the second blade driving lever 35. Thecam profile 80a is formed at a position at which the cam follower 39abuts against the cam profile 80a before the second blade driving lever35 reaches the end of forward movement and the shape of the cam profile80a is formed so that the tangent of the moving locus formed by the camfollower 39 just before the cam follower 39 comes into contact with thecam profile 80a intersects the cam profile 80 a at an obtuse angle. Suchstructure is the same as that of the cam 60 for the first blade group.However, the angle of the cam profile 80a can be finely adjusted byrotating the cam plate 80 about the shaft 34 by a very small angle asdescribed above. The cam profile 80a performs the same operation as thatof the second profile portion 40a of the groove cam 40 of the firstembodiment.

Accordingly, even in the second embodiment, the force of the springs 17and 37 is transmitted to the driving levers 15 and 35 through thereversing levers 16 and 36 as the propelling force until the camfollowers 19 and 39 reach the cam profile portions 60a and 80a while theforce of the springs 17 and 37 is transmitted to the driving levers 15and 35 through the reversing levers 16 and 36 as a braking force afterthe cam followers 19 and 39 have reached the cam profile portions 60aand 80a, so that shock and oscillation at the end of forward movementare reduced.

As described above, according to the present invention, since the singlespring is utilized as a source of driving force for moving the shutterblades until the middle of the movement of the shutter blades, and isutilized as a source of force for braking the shutter blades after themiddle of the movement of the shutter blades, it is not necessary toprovide a separate braking spring and space for accommodating a brakingmechanism unneeded.

Further, according to the present invention, since the shock absorptionmechanism does not have any member exerting friction, the shockabsorption mechanism is not affected by variation of the coefficient offriction due to variation in temperature, and a stable aperturecharacteristic of the shutter can be attained regardless of theenvironment of use of the camera. Further, the shock absorptioncapability of the shock absorption mechanism is not reduced by wearingof a friction member.

In addition, as described above, in the present invention, since thespring for driving the shutter is operated as the source of force forbraking the shutter, it is not necessary to provide a braking mechanismseparately from the shutter driving mechanism and an increased amount ofset force is not needed.

Furthermore, in the present invention, since only the reversing lever isadded to the mechanism and a setting roller can use the cam followermounted on the reversing lever, the structure is extremely simple.

If the passing locus of the cam follower is set to be an obtuse angle ata point at which the passing locus varies from the arcuate locus of thedriving lever about the rotation axis to the direction of separatingfrom the axis of the driving lever, a member for producing substantialcollision is not provided and wearing due to collision is extremelyreduced.

Further, if the mounting position of the cam plate can be adjusted,adjustment can easily be made so that ideal shock absorption performanceis attained within a range capable of moving the blade groups to the endof forward movement exactly and adjustment of the shock absorptionperformance during repair or the like can be easily made.

We claim:
 1. A driving mechanism for a focal plane shutter comprising:ablade group including a plurality of individual blades for closing anexposure aperture formed in a shutter base plate by spreading saidplurality of blades from an overlapped state and for opening saidaperture by overlapping said plurality of blades from a spread state; adriving lever swingably mounted around a shaft on said base plate andcoupled with each of said plurality of blades constituting said bladegroup to move said blades between the spread state and the overlappedstate; a reversing lever swingably mounted on a shaft on said drivinglever at a position different from the shaft on which said driving leveris mounted and being rotatable in a restricted relative rotation rangewith respect to said driving lever; a cam follower mounted on saidreversing lever between the shaft on which the reversing lever ismounted and a free end of said reversing lever; energizing means havingan operation end engaged with the free end of said reversing lever tourge said reversing lever in a direction for moving said driving levertoward an end of forward movement of said driving lever; releasing meansengagable with said driving lever for releasing said driving lever froman initial position thereof; and a cam means having a cam profile withwhich said cam follower is engaged and including a first profile portionfor leading said cam follower along an arcuate locus about the shaft onwhich said driving lever is mounted in a former part of movement of saiddriving lever from the initial position thereof to the end of theforward movement thereof, and a second profile portion for restrainingrotation of said cam follower about the shaft on which said drivinglever is mounted in a latter part of the movement of said driving leverfrom the inital position to the end of forward movement thereof.
 2. Adriving mechanism as claimed in claim 1 in which tangent lines to saidcam profile portions at a point where said first profile portion isjoined to said second profile portion intersect at an obtuse angle.
 3. Adriving mechanism as claimed in claim 1 in which said cam means is a camopening in said shutter base plate.
 4. A driving mechanism as claimed inclaim 3 in which tangent lines to said cam profile portions at a pointwhere said first profile portion is joined to said second profileportion intersect at an obtuse angle.
 5. A driving mechanism accordingto claim 1 further comprising a set lever means connected to saiddriving lever for moving said driving lever from the end of the forwardmovement thereof to the initial position of the driving lever, said setlever means being engaged with said cam follower during said moving ofsaid driving lever.
 6. A driving mechanism for a focal plane shuttercomprising:a blade group including a plurality of individual blades forclosing an exposure aperture formed in a shutter base plate by spreadingsaid plurality of blades from an overlapped state and for opening saidaperture by overlapping said plurality of blades from a spread state; adriving lever swingably mounted around a shaft on said base plate andcoupled with each of said plurality of blades constituting said bladegroup to move said blades between the spread state and the overlappedstate; a reversing lever swingably mounted on a shaft on said drivinglever at a position different from the shaft on which said driving leveris mounted and being rotatable in a restricted relative rotation rangewith respect to said driving lever; a cam follower mounted on saidreversing lever between the shaft on which the reversing lever ismounted and a free end of said reversing lever; energizing means havingan operation end engaged with the free end of said reversing lever tourge said reversing lever in a direction for moving said driving levertoward an end of forward movement of said driving lever; releasing meansengagable with said driving lever for releasing said driving lever froman initial position thereof; and a cam means having a cam profilepositioned in a path of movement of said cam follower around the shafton which said driving lever is mounted and having a cam profile forrestraining movement of said cam follower along said path and beingengaged by said cam follower as said cam follower is moving along saidpath as said driving lever is moving from the initial position towardthe end of forward movement, said position being at a point reached bysaid cam follower before said driving lever reaches the end of forwardmovement thereof.
 7. A driving mechanism as claimed in claim 6 in whicha tangent to said cam profile intersects a tangent to the path ofmovement of said cam follower at an obtuse angle.
 8. A driving mechanismas claimed in claim 6 in which said cam means comprises a cam plateadjustably mounted on the shutter base plate.
 9. A driving mechanism asclaimed in claim 8 in which a tangent to said cam profile intersects atangent to the path of movement of said cam follower at an obtuse angle.10. A driving mechanism according to claim 6 further comprising a setlever means connected to said driving lever for moving said drivinglever from the end of the forward movement thereof to the initialposition of the driving lever, said set lever means being engaged withsaid cam follower during said moving of said driving lever.